Line Narrowing in Photoemission by Coincidence Spectroscopy

Abstract

We present photoemission spectra from the 3p level of Cu(lOO) obtained in coincidence with the MiW Auger line. The 3p level is narrowed from its 2.2-eV core-lifetime-broadened width to 1.0 eV, representing the intrinsic width of the l G Auger final state. The core line changes its energy within the 2.2-eV envelope as the Auger coincidence energy is changed, conserving the sum of Auger-electron and photoelectron kinetic energies.PACS numbers: 79.60.Cn, 71.50.+t Auger-photoelectron coincidence spectra were first reported by Haak and co-workers. 1 Many potential enhancements of ordinary photoelectron and Augerelectron spectroscopies are described in the original papers. l Most are based on the extra discrimination provided by knowing which subpeak in the Auger spectrum is associated with which subpeak in the photoelectron spectrum. Also suggested was the possibility that corehole lifetime broadening could sometimes be eliminated from the photoelectron spectrum. This is an especially exciting possibility, because the short Auger decay lifetime of core holes in solids can lead to broadening of more than an eV, obscuring interesting structure associated with chemical shifts, surface shifts, many-body structure, line shape, etc. 2 Poor instrumental energy resolution has previously prevented an experimental verification of this suggestion. In this paper we present data from the Cu(lOO) 3p core line in coincidence with the M3W (3p3d3d) Auger line illustrating this effect. The 3p linewidth is narrowed from 2.2 to 1.0 ±0.2 eV. We believe that this 1.0 eV is the lifetime width of the l G Auger final state.In this technique two electron energy analyzers are focused on one x-ray or uv illuminated sample. One analyzer is tuned to the energy of a core photoelectron and the other is tuned to an appropriate Auger decay energy. An event is recorded only when electrons are received in each analyzer simultaneously. This is interpreted to mean that both electrons are associated with the same photoexcitation event. Experimental details will be provided in another paper. 3 Briefly, commercial double-pass cylindrical-mirror analyzers 4 were set to 60-eV pass energy with 1-mm (small) apertures. One was fixed at a characteristic Auger energy, and the other was swept through the photoelectron spectrum. The 150-eV light from the National Synchrotron Light Source vacuum ultraviolet ring, was monochromatized by the U14 plane-grating monochromator. 5 The energy resolution, electron plus photon, in each system was <0.5 eV. The Auger (photoelectron) analyzer pulses provided starts (stops) for a time to amplitude converter. The output from the converter was analyzed by a multichannel analyzer. This provided output pulses for zero time delay (coincidence) and 180-ns time delay, each ±10 ns. The 180-ns delay pulses (one revolution time in the storage ring) were used to subtract accidental coincidences from the spectra. The sample was sputtered and annealed once per day. No contamination was visible in electron stimulated Auger spectra. Each coincide...

New insight into the Auger decay process in O2: The coincidence perspective

“…One example for which numerous electron-electron coincidence studies have been performed is inner shell photoionization followed by the emission of an Auger electron. After the first successful experimental study of this problem by T. Darrah Thomas and co-workers [1] other authors followed, both in the solid state [2][3] [4] and the atomic and molecular physics communities [5] [16]. A somewhat more detailed overview has been given in Ref.…”

Auger Photoelectron Coincidence Spectroscopy

“…Hence Haak (1983) was able to show the Cu component of the CuNi Auger line from the alloy. Jensen et al (1989) have used a variation of the APECS experiment to determine the shape of the 3P photoelectron peak in Cu in coincidence with the MVV Auger line. They illustrated the fact that the photoelectron line energy changed as the energy of the Auger analyser was varied.…”

“…The size of the background subtracted peak can be stored as a point corresponding to the settings of the two analysers. Jensen et al (1989) used a synchrotron as a source and used the time structure of the photon pulses to provide a convenient means of getting good timing resolution (::::20 ns). They also used conventional double-pass cylindrical mirror analysers (CMA) to energy analyse the electrons in each channel.…”

Linear magnetic and alignment dichroism in Auger–photoelectron coincidence spectroscopy

“…In molecular physics, on the other hand, these electron-electron coincidence measurements of core-level ionization [4] enable one to disentangle the contribution of the different vibrational levels and of the atoms in different sites, to the molecular Auger spectrum. In solid state physics the technique of Auger-photoelectron coincidence spectroscopy (APECS) has proved to be successful in studying complicated Auger spectra [17][18][19]. APECS measurements for solid targets are site-specific and show an increased surface sensitivity in comparison with conventional one-electron experiments as well as a strong reduction of secondary electron background.…”